The term "polyphenylene ether resin" includes a family of polymers well known to those skilled in the art, and they are made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene ethers are disclosed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. In The Hay patents, the polyphenylene ethers are prepared by an oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes for preparing polyphenylene ether resins, including graft copolymers of polyphenylene ethers with styrene type compounds, are found in Fox, U.S. Pat No. 3,356,761; Sumitomo, U.K. Pat. No. 1,291,609; Bussink et al., U.S. Pat. No. 3,337,499; Blanchard et al., U.S. Pat. No. 3,219,626; Laakso et al., U.S. Pat. No. 3,342,892; Borman, U.S. Pat. No. 3,344,166; Hori et al., U.S. Pat. No. 3,384,619; Faurote et al., U.S. Pat. No. 3,440,217; and disclosures relating to metal based catalysts which do not include amines, are known from patents such as Wieden et al., U.S. Pat. No. 3,442,885 (copper-amidines); Nakashio et al., U.S. Pat. No. 3,573,257 (metal-alcoholate or -phenolate); Kobayashi et al., U.S. Pat No. 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al., U.S. Pat. No. 3,382,212. Cizek, U.S. Pat. No. 3,383,435 discloses polyphenylene ether-styrene resin compositions. All of the above-mentioned disclosures are incorporated herein by reference.
One of the outstanding properties of the polyphenylene ether resins is the property of high-heat resistance which makes possible the use of this resin in applications where many thermoplastics would fail. This exceptional property, while desirable in a finished article, causes problems when melt blending is used to form compositions that include the polyphenylene ether resins. One problem is related to the fact that the high temperatures required for the processing of the polyphenylene ethers approach the temperatures at which additives begin to degrade. Materials such as alkenyl aromatic resins fall within this class. This fact has made it desirable to find a material that will allow lower blending and molding temperatures to be used without adversely affecting the properties of the molded article. It has now been found that if certain compounds such as phthalates and phosphates are first blended with a polyphenylene ether resin, to form a preblend, the preblend may be further processed at temperatures that are substantially below the softening temperature of the polyphenylene ether resin.
In the prior art, compositions which have included a polyphenylene ether resin, a phosphate compound and an alkenyl aromatic resin are known. These compositions are disclosed in U.S. Pat. No. 3,639,506. However, these compositions have been prepared by first dry blending all of the components and extruding the composition at the temperature which is necessary to cause the polyphenylene ether resin to flow. This method of preparing the composition often results in a "pock marked" product that is due to "unmelted" polyphenylene ether resin which did not achieve a low enough viscosity to intimately combine with the other components of the composition. The present invention overcomes this problem as the preblend of the polyphenylene ether resin and the compound that reduces the alloying temperature of the polyphenylene ether resin alloys with the alkenyl aromatic resin to form a very uniform composition at a temperature that does not degrade any of the components of the composition.
It is, therefore, a primary object of this invention to provide an improved method of preparing compositions of a polyphenylene ether resin and an alkenyl aromatic resin.